Of motors to be mounted in vehicles, a motor to be used for driving a vehicle is demanded for compact size and high output power. Therefore, it has been studied to form a coil of a flat conductor having a rectangular cross section effective in increasing a lamination factor. When a coil is to be formed of such a flat conductor, however, the flat conductor having a large cross sectional area is hard to be wound into a coil shape. Further, the flat conductor having a large cross sectional area can increase current density, but may cause a problem with eddy current. Accordingly, various studies have been made to form a coil by winding a flat conductor.
Patent Document 1 discloses a litz wire coil formed of a rectangular litz wire wound to be vertically stacked in an axial direction to be wound in two layers, forming in turn an outside layer, an inside layer, an inside layer, and an outside layer.